Article at AustralianMining.com
A strong and stable standing roof support that can handle the high deformation of tailgate environments is imperative to all longwall mines worldwide. In 1993, USA-based Strata Products Worldwide introduced a revolutionary timber support prop engineered to safely yield under load and effectively accommodate convergence of the roof and floor. This ability of the Propsetter® to yield in a controlled manner prevents the support system from catastrophically breaking or snapping under load – a problem often seen with traditional static posts. After years of proven success in US coal mines, Strata introduced the Propsetter® to the Australian mining market in 1996, bringing to the industry the lowest cost-per-support-ton roof support available.
The Propsetter® offers support capacities matching those of four-point chocks, while at the same time significantly reducing the amount of material handling required and ventilation resistance experienced with bulky chocks. They are used predominantly as tailgate support, but are also very effective in longwall shield recovery and long-term bleeder support. The standard 215mm-diameter unit has a load capacity of 45 tonnes, while the larger 250mm-diameter unit’s load capacity is 55 tonnes.
The design of the Propsetter® utilizes the timber’s strength and orthotropic properties to achieve desirable rock mechanic features such as initial stiffness and controlled roof and floor yield. Various Strata-supplied pre-stressing devices can be used with the props, creating effective roof and floor pre-loading, which results in active support. The Strata Hydrocell, for instance, is an expandable sheet metal plate placed atop the prop during installation and filled with water. As Hydrocell expands, it produces active support load, reinforcing the roof strata and increasing the Propsetter’s resistance to lateral loads, such as those caused by rib deterioration. The Strata PowerWedge is a mechanical pre-stressing device that converts torque into upward roof force, generating pre-stressing loads up to 10 tonnes. The torque can be applied with either a 29mm socket and hand wrench, or an air or hydraulic tool. The PowerWedge is a standalone device and does not require water, grout or pumps.
The size, shape and specialized packaging of Propsetters and Propsetter systems enable many more units to be loaded and transported on a supply car compared to chocks, and installation is very fast and significantly easier than its rivals, with the ability to install up to 150 units in a single work shift.
“We set 1200 feet (365 meters) of Propsetters in six shifts,” stated a longwall coordinator at a West Virginia coal mine. “That was with six guys doing it manually.”
Strata offers customized packaging according to customer needs, including all system components (prop, headboard and footboard) bundled together for efficient handling and transport